Electrical control system for fluid



March 1, 1938. E. M. MILLER 2,110,049 I ELECTRICAL CONTROL SYSTEM FORFLUID FUEL BURNERS Filed Dec. 16, 1932 ROOM THER OSTAT II c b 59 Je-/-r/o- 57- v 32 BURNER MOTOR 64 H W fifi 64 f 36 2L [5 4 I6 COMBUSTIONRBsPoNsIvE SWITCH OPEN cow INVE-NTOF? ATTORN y Patented Mar. 1, 1938CONTROL SYSTEM FOR FLUID FUEL BURNERS ELECTRICAL PATENT' OFFICE ErnestM. Miller, Minneapolis, Minn, assignor to Minneapolis-HoneywellRegulator Company, Minneapolis, Minn., a corporation of DelawareApplication December 16, 1932, Serial No. 647,588

3 Claims.

The present invention relates to electrical systems of control for fluidfuel burners of the type that discontinue operation of the fluid fuelburner until manual intervention if combustion fails after successfulinitial ignition, as distinguished from those control systems for fluidfuel-burners in which the controls recycle'to attempt a reignition ofthe fuel under similar circumstances.

The failure of combustion after successful initial ignition and in theabsence of power failure (commonly known as a flame failure) in a fluidfuel burning .system very often indicates that there is a defect in theelectrical control system. Many manufacturers prefer to have the entirefuel. burning system shut down on a flame failure until the system hasbeen inspected and repaired, if necessary, instead of having the systemattempt to re-ignite the fuel.

Many systems of electrical control for fluid fuel burners that include aswitching-mechanism responsive to combustion conditions and in whichthere is provision whereby operation of theburner is discontinued untilmanual intervention upon the occurrence of a flame failure, haveheretofore been proposed. However, all of these prior :rt systems havehad certain objectionable feaures.

In one type ofsuch prior art systems, it is necessary to use threeelectrical relays which is objectionable as to. cost. In another type'of such systems, one of the relays is dispensed with, but it isnecessary to provide a mechanical inter-locking switching mechanismjointly operated by the two remaining relays, or else it is necessary touse a complicated combustion responsive switching mechanism whichdirectly controls the high voltage ignition circuit besides performingits other functions.

It is a general object of this invention to provide an improved burnercontrol system in which the burner operation is discontinued until thereis manual resetting of a safety device upon the occurrence, of flamefailure.

More particularly, one of the objects of the present invention lies inthe provision of an electrical control system for fluid fuel burnersincluding. only two relays, no mechanical' interlocking switchingmechanism, and a simple combustion responsive switch that does notdirectly control thehigh voltage ignition circuit, which control systemoperates to discontinue burner operation until manual intervention on aflame failure.

Many of the electrical control systems for fluid f u'elburners now inuse include an electrically heated time switch which renders the entiresystem inoperative if ignitioni. e.,initial combustion when the burneris started-is not successful. Some of these systems, upon the occurrenceof a flame failure, mechanically prevent the return of ignition and stopthe burner motor by re-energizing the electrically heated time switch.When there is a flame failure in such a system, fluid fuel continues toflow into the fire-box after the combustion responsive member hasresponded to the flame failure and until the electrically heated timeswitch is opened as a result of its being energized for a predeterminedlength of time. A system of this type is objectionable in that acomparatively large amount of unconsumed fuel is deposited in thefire-box between the time of the flame failure and the shut down by theelectrically heated time switch. The time lag between the action of thecombustion responsive device and the shutting off of the oil supply isequal to the period ,allowed for ignition to take place initially.

- One of the more specific objects of the invention is the provision ofan electrical control system for fluid fuel burners of the general typediscussed above in which the interval between action of a flame failureresponsive device and the shutting off of the burner motor is less thanthe initial ignition period, whereby a decreased amount of unconsumedfuel is deposited in the fire-box. Specifically, this resultisaccomplished in the embodiment of the invention hereinafter described byincreasing the current flow to the electrically heated time switch whenthere is a flame failure. Return of ignition after such a flame failureis also prevented, but this is accomplished entirely electrically anddispenses with all mechanical locking mechanisms. A further object ofthe invention is the pro- Vision of an electrical control system whichoperates in the manner above described and, in addition, recycles ifthere is a failure in the supply of electrical power, so as to attemptto re-ignite the fuel when power is restored.

Further objects of the invention will become apparent as the descriptionthereof proceeds.

For a -more complete understanding of the invention,'reference may behad to the following description and accompanying .single drawing whichis a schematic wiring diagram of one embodiment of the presentinvention.

Referring to the drawing, an electrically operated fuel supplycontrolling device herein discated at H. The burner motor l0 andignition means II are controlled by an electrical control system thatincludes a main switch herein specifically shown as a room thermostatl2, a time operated switching mechanism 3, first and second relays I4and I5, and a combustion responsive switching mechanism l6.

The room thermostat or main switch l2 comprises a bimetallic element llone end of which is secured as shown at l8. The free end of bimetallicelement controls contact blades l9 and 20 in such a manner that contactblade l9 first engages a contact 2| and then contact blade 20 engages acontact 22 upon a lowering in the temperature to which bimetallicelement I7 responds. When this temperature rises, bimetallic elementfirst moves contact blade 20 out of engagement with contact 22 andthereafter moves contact blade I9 out of engagement with contact 2|.

The time operated switching mechanism l3 may be-of any of the well-knowntypes in which a normally closed switch 23, which is thermostaticallycontrolled, is moved to open. position and latched therein when itsassociated thermostatic element 23a hasxbeen heated to a predetermineddegree. An electrical heating coil 24 is associated with switch 23 so asto heat its thermostaticelement 23a to a predetermined degree when theelectrical heating coil 24 has been traversed by a predetermined currentflow for a predetermined length of time.

Relay |4 comprises a relay coil 25 which controls an armature 26. Whenrelay coil 25 is energized, armature 26 is attracted and moves switcharms 21, 28, 29 and 30 respectively into engagement with contacts 3|,32, 33, and 34.

Upon deenergization of relay coil 25, armature- 26 moves under theinfluence of gravity to the and switch arms 39 and 40 respectively outof position shown in the drawing wherein switch arms 21, 28, 29, and 36are out of engagement with contacts 3|, 32, 33, and 34. Relay I5,likewise, comprises a relay coil 35 which, when energized, attracts anarmature 36 thereby moving switch arm 31 into engagement with contact 38nism l6 comprises a switch arm 43 which is out of engagement with acontact 44 when combustion is absent and moves into engagement therewithupon the successful establishment of combustion. The switch arm 43 maybe controlled by combustionconditions in any desirable manner but it ispreferably thermally controlled by the heat of combustion through anon-positive transmission mechanism, such, for instance, as shown in CyrPatent 1,768,892. I

Electrical power for the various electrical devices and control circuitsis supplied by line wires 45 and 46 and a step-down transformer 41. The

primary 48 of the step-down transformer 41 is connected to line wires 45and 46 by wires 49 and 50'. The low voltage secondary is indicated at5|. The various circuit connections will be described under the headingoperation.

' operation When the temperature to which bimetallic element respondsbegins to .fall contact blade l9 will first engage contact 2|, butthis-engagement will not result in the completion of any electricalcircuits. As the temperature to which bimetallic element continues tofall contact blade 29 will engage contact 22 which will result inenergization of relay coil 25 and electrical heating coil 24 as follows:secondary 5| wire 52, switch 23, wire 53, contact 2|, contact blade l9,contact blade 20, contact 22, wire 54, switch arm 40, contact 42, wire55, wire 56, electrical heating coil 24, wire 5?, relay coil 25, andwire 58, back to secondary 5|. Energization of electrical heating coil24 will result in heating of the thermostatic element which controlsswitch 23. Energization of relay coil 25 will attract armature 26 tomove switch arms 21, 28, 29 and 36 into engagement with contacts 3|, 32,33, and 34 as heretofore described. Engagement of switch arms 21 and 26with contacts 3| and 32 establishes energizing circuits for burner motorIn and ignition means The circuit for burner motor I0 is as follows:line 45, wire 59, contact 32, switch arm 28, wire 60, switch arm 21,contact 3|, wire 6|, burner motor l9, and wire 62, to line 46. Theenergizing circuit for ignition means I is as follows: line 45, wire 59,contact 32, switch arm 28, wire 69, wire 63, contact 4|, switch arm 39,wire 64, ignition means H, and wire 65 to line 46. Engagement of switcharm 29 with contact 33 establishes a holding circuit for relay coil 25which is independent of contact 22 and contact blade 20. This holdingcircuit is as follows: secondary 5|,-52, 23,

53, contact 2|, contact blade l9, thermostatic element I7, wire 66, wire61, contact 33, switch arm 29, wire 68, 56, electrical heating coil 24,51, relay coil 25, and 58 to secondary 5|. Engagement of switch arm 36with contact 34 partially establishes a circuit which ,will be describedhereafter.

' The burner motor In is now operating to supply fuel to the burner andignition means H is energi'zed for the purpose of igniting the fuel thussupplied. Electrical heating coil 24 is heating the thermostatic elementwhich controls switch 23. If combustion should not be successfullyestablished withinthe predetermined time, switch 23 will be opened andlatchedin open position thereby deenergizing electrical heating coil 24and relay coil 25. Deenergization of relay coil 25 will in turndeenergize burner motor I!) and ignition means I The whole system istherefore shut down until the switch 23 is manually reset.

Assuming that combustion is successfully established within thepredetermined time, switch arm 43 will move into engagement with contact44 to establish an energizing circuit for relay coil 35 as follows:secondary 5|, 52, 23, 53, contact 2|, contact blade I 9, thermostaticelement wires 66, 69, contact 44, switch arm 43, ,wire

l9, relay coil 35, wire 1|, and 58 to secondary 5| In addition to thecircuit just traced, it will be noted that relay coil 35 could be alsoenergized upon the establishment .of combustion through contact 42 andswitch arm 40 but this circuit would be immediately broken uponseparation of switch arm 40 from contact 42. KIhis circuit is asfollows: secondary 5|, 52; 23,53, contact 2|,

contact blade l9, contact blade 20, contact 22,

54, switch arm 40. contact 42, 55, 68, switch arm 29, contact 33, 61,69, contact 44, switch arm.

43, 19, relay'coil 35,- TI, and 58 to secondary 5|. Energ zation ofrelay coil 35 attracts armature 36 which moves switch arm 3'! intoengagement with contact 38 and switch arms 39 and 49 out of engagementwith contact 4| 'and 42. Movement of switch arm 40 out of engagementwith contact 42 interrupts the last described energizing circuit forrelay coil 35 and likewise interrupts the original .energizing circuitfor relay coil 25. Relay coil 25 will be maintained energized, however,by the holding circuit previously described. Disengagement of switch arm39 from contact 4| interrupts the circuit to ignitionmeans Engagement ofswitch arm 31 with contact 38 shunts electrical heating coil 24 toestablish a. new circuit for relay coil 25 as follows: secondary 5|, 52,23, 53; contact 2|, contact blade l8, thermostatic element |1, wire 66,

69, contact 44, switch arm 43, 18, wire 12, contact 34, switch arm 30,wire 13, switch arm 31,

-atively deenergized by means of the shunt circuit just described. Whenthe room temperature rises contact bladewill first disengage contact 22but the system will remainin operation. On a further rise in roomtemperature contact blade IE! will disengage contact 2| interrupting thecircuits to relay coils 25 and 35. Deener'gization of relay coils 25 andwill allow their respective armatures 26 and 36 to return to theposition shown in the drawing under the influence of gravity and theentire system will therefore be shut down.

If there should be a flame failure while the system is operatingnormally as above described, switch arm 43 will disengage contact 44.Relay -coils"25 and 35 will remain energized but will now k be connectedin parallel and the full flow of current to both of these relay coilswill pass through electrical heating coil /24. This series parallelcircuit is as follows: secondary 5|, 52, 23, 53, contact 2|, contactblade I9, thermostatic element 1, 66, 61, contact 33, switch arm 29, 68,56, electrical heating coil 24 to 51 at which point the circuit willbranch, part of the current going by way of relay coil 25 and 58 tosecondary 5| and the other part going by way of 14, contact 38, switcharm 31, 13, switch arm 30, 34,

12, relay coil 35, 1|, and 58 to secondary 5|.

-The resulting current flow through heating coil 24 will be considerablylarger than the normal current flow therethrough when only relay coil 25is in series therewith, with the result'that switch 23 will be openedand latched in open position in a much shorter time than would be thecase if combustion were not successfully estabfuel to the burner and theignition means II will be maintained deenergized. Although this system.permlts the depositing of a certain amount of unconsumed fuel into thefire-box after a flame failure it is to be. noted that a much largeramount would be deposited therein if the time operated switchingmechanism 3 were allowed to open only after the normal predeterminedtime period had expired; This system, therefore, diminishes the amountof unconsumed fuel that may be deposited in the fire-box after a flamefailure by shortening the timing period of the time-operated switchingmechanism so that it operates more quickly than it would under I normalconditions wherein combustion was not v initially established.

At this time, it would be well to explain the utility of switch arm 21and contact 3|. When relay coils 25 and 35 are de-energized as theresult of opening of switch 23 after a failure of flame, switch arm 39will move into engagement with contact 4| and switch arm 28 willdisengage contact 32. If switch arm 21 and contact 3| were omitted, acomplete electrical circuit would thereby be established from motor |8through ignition means H as follows: motor I8, wire 6|, wire 63, contact4|, switch arm 39, wire 64, ig-

nition means wire 65, line 46 and wire 62 backto motor in. The motor ID,will coast for a short time after de-energization as the result ofswitch arm 28 moving out of engagement with contact 32 and in coastingwill generate an electro-motive force which would momentarilyre-energize ignition means II by the abovedescribed circuit if switcharm 21 and contact 3| were omitted. This momentary re-energization ofignition means I| would very likely ignite the unconsumed oil and/or oilvapors which collected in the combustion chamber after the occurrence ofthe flame failure and cause an explosion. This hazardous'conditioniseliminated by the insertion of switch arm 21 and contact 3| betweenmotor IO and ignition means I I. If the system is operating normally andthe supply of electrical power should fail, relay coils 25 and 35 wouldbe deenergized and the system would return to its inoperative positionas shown in the drawing. If the power should immediately return beforeswitch arm 43 has disengaged contact 44 and if contact blades l9 and 2Bare in engagement with their respective contacts 2| and 22, there willbe energizing circuits for both relay coils 25 and 35. Armature 36 willbe attracted first, however, partly by reason of the adjustment of thecontact pressures and partly by reason of a smaller air gap. Theenergizing circuit for relay coil 25 will be interrupted at 40, 42before its armature-26 has been attracted. Relay coil 35, therefore,remains energized until switch arm 43 disengages contact 44 whereuponthe system will recycle and initiate a new trial ignition period duringwhich combustion will either be successfully established or the systemwill be shut down until manual intervention. If the power 4 failureshould last until after switch arm 43 disengages contact 44, the systemwill recycle in an attempt to establish combustion just as soon as ,theelectrical power returns.

" From the foregoing description, it will be apparent that thisinvention provides a simple electrical )control system for fluid fuelburners in which the entire system is rendered inoperative until manualintervention if the flame should fail after combustion has beeninitially successfully established. This system requires only twoelectrical relays and utilizes a simple single circuit combustionresponsive switching mechanism and does away with all mechanical lockingmechanisms operated either by the combustion responsive switchingmechanism or one or more of the relays. In addition, this systemprovides for a recycling upon a failure of electrical power whether thispower. failure be momentary or for a substantial length of time.

' While a specific embodiment of the invention has beenherein'illustrated and described, it is to be understood that variouschanges and modiflcations can be made and I intend to be limited only inthe purview of the appended claims.

. I claim as my invention:

1. A system of the class described, comprising,

in combination, a thermostatically controlled switch adapted to beopened and latched in open position when heated to a predetermineddegree, an electrical heating element therefor, a main switch, a firstelectro-magnetic device, switching mechanism operated thereby, a secondelectro-magnetic device switching means operated thereby, a singlecircuitcombustion responsive switch open during the absence ofcombustion, an electrically operated fuel supply controlling device,electrically controlled ignition means, a

series circuitfor initially energizingthe first electro-magneticv deviceand electrical heating element through the thermostatically controlledswitch upon closure of the main switch, the current flow thus producedthroughthe heating element being sufiicient to open the thermostaticallycontrolled switch after a predetermined length of time, circuits for thefuel supply controlling device and ignition means closed by saidswitching mechanism upon energization of the first electro-magneticdevice, an energizing circuit for the second electro-magnetic deviceincluding the thermostatically controlled switch, main switch andcombustion responsive switch in series, said switching means thereuponinterrupting the cit"- cult to the ignition means, a. shunt circuit forthe electrical heating element established by said switching means uponenergization of the second electro-magnetic device, saidelectro-magnetic devices when energized effecting operation of saidswitching means and switching mechanism to complete a circuit connectingsaid electro magnetic devices in parallel with each other and in serieswith said heater and a shunt circuit for said heater including saidcombustion responsive switch whereby, upon opening of said combustionresponsive switch with said electro-magnetic devices energized thecurrent flow through said heater is materially increased over theinitial current flow therethrough, thereby opening said safety switch ina time period materially less than said predetermined time through saidelectrical heating element to quickly open the thermostaticallycontrolled switch and deenergize said electro-magnetic' devices.

2. In a system having electrically controlled fuel feeding and ignitionmeans, a main control switch, an electrically actuted time limit cut-outswitch operable to open in time periods varying in accordance with itsrate of energization, switching mechanism including reactances and acombustion controlled switch, and circuit connections including theforegoing elements controlling energization of the fuel feeding and lgnition means and the energization of the time switch and rate thereofand operable upon a demind for heat and closure of the main switch to:,(1) energize the fuel feeding and ignition means and energize the timeswitch at a predetermined rate: (2). deenergize the ignition means andtime switch upon the establishment of combustion; and (3) reenergize thetime switch at safety time switch whose timing interval varies fwith-the rate at which it is energized for discontinuing fuel feed tothe burner at the conclusion-of its timing interval, a combustionresponsive device, and means responsive to the maincontrol member forsimultaneously initiating operationof saidburner and ignition means andenergizing said time switch at a first rate, and cooperating with thecombustion responsive device to deenergize said time switch andignition:

means upon the successful establishment of com-- bustion, and toreenergize said time switch at a second'rate higher than said first rateupon the occurrence of subsequent flame failure, where-- by said timeswitch provides a longer timing interval upon initiation of operation ofthe burner than 'is provided upon the occurrence

